1. Field of the Invention
The present invention relates to a developing device for developing an electrostatic latent image in an image forming apparatus such as an electrophotographic copying machine or printer.
2. Description of the Background Art
The electrophotographic image forming apparatus generally produces an intended image in such a manner that an electrostatic latent image is formed, e.g., by effecting an image exposure corresponding to an original image on an electrostatic latent image carrier such as a photosensitive member, and then is developed by a developing device into a visible image, which is transferred and fixed onto a record member.
Various developing devices of the above type have been proposed and employed. These devices usually include developing rollers. The developing roller carries a thin film of developer supplied thereto, and rotates to transfer the developer carried thereon to a developing region, at which the developing roller and the electrostatic latent image carrier are opposed to each other, for developing the electrostatic latent image.
The developing device is also provided with means for preventing leak of the developer.
This developer leak preventing means is arranged at a portion(s) where the developer may leak. In connection with the developing roller, these means are employed for preventing leak of the developer from the opposite ends of the roller. Particularly, in the developing device having the developing roller which is in contact with the electrostatic latent image for developing the same, the leak preventing means are provided for preventing movement of surplus developer from the ends of the developing roller onto the electrostatic latent image carrier. As the above means, such as structure has been known that an arc-shaped sealing member arranged within the developing device is in contact with a surface of each end of the developing roller facing to the interior of the developing device.
This sealing member is in contact with the roller end in such a manner that the member does not impede rotation of the developing roller but can prevent the developer from entering an area between the surface of the roller end and the sealing member and leaking therefrom. It has been recognized that the member can achieve a developer leak preventing effect to some extent. However, it is now desired to prevent leak of the developer more reliably.
The reason is as follows. In the present devices, developer may enter the space between the sealing member and the developing roller. The developer in the space gradually solidifies in accordance with rotation of the developing roller, and thereby increases the gap between the sealing member and the developing roller, so that the developer externally leaks to cause problems such as smearing of an interior of the image forming apparatus. Also, the quantity of the developer in the space is impaired due to rubbing against the rotating developing roller so that the developer of the impaired quality causes a so-called fogging phenomenon at the end of the electrostatic latent image carrier, resulting in a problem that the quality of the image transferred onto the record member is impaired.